Private automatic exchange system



Jan. 27, 1931. T. F. CROCKER iRIVATE AUTOMATIC EXCHANGE SYSTEM FiledFeb. '29, 1928 2 Sheets-Sheet 1 CG PAX In 1" 1.ren ur Thomas F CrackerJan. 27, 1931.

T. F. CROCKER PRIVATE AUTOMATIC EXCHANGE SYSTEM Filed Feb. 29, 1928 2Sheets-Sheet 2 Im Thomas F Cracker Patented Jan. 27, 1931 l PTA-TENT.oFF-Ica live 0,091...

magm s. cnocxnn, QECHICAGO; rumors; nssieivonmo nnsnnvn HOLDING coin.PANY OFBKANSASIZCITYQMISSOUBI, A conrone'r en or DELAWARErnwnrnnuroiymric nxcnnncn SYSTEM Application filedlebruary 29, 1928."Serial No. 258,108..

type having a cord-splitting key by means 7 of which the attendant,after setting up a connection to a called; subscribers line at therequest of a calling; subscriber, mayconverse with thecalled subscriberwithout the calling subscriber hearingthe conversation. A par- 2 ticularfeature of this invention is the provision of means in the cord;circuitwhich re- .quiresthe attendant to press. a special connectkeybefore the actual talking circuit betweenthe called and the callingsubscriber can be establishechthough sheinay converse.

with either separately before operating the special connect key.

Another feature of this invention is. that 1 should the attendant notcare to converse -with the called subscriber separately beforecompleting the talking connection abetween thecalling and the calledsubscriber, she may operate thevspecial con-nect key immediatelyso'that," the talking, connection between the calling and the calledsubscriber will be automatically completed as soon as the calledsubscriber answers.

Another; featu-reof this invention is that d after a connectionhas beenset up and the 4 talking connection can again be completed with thefirst calling party, should the called party again remove his receiver,until the special connect key is again operatedattendant is. employedcalled party has hung up. his receiver, 110- Another feature of thisinvention resides in the arrangement for preventing the application. ofringing current on a 'busy line on a called line] after the calledsubscriber has answered, or for preventing any interference with thesetting up of a connection,.shouldjthe attendantinsert theplugof hercord into a busy line jack andattempt to ring, or attempt to ring aftera called subscriber hasanswered, or insert the plug of her'cord into abusy trunk 'j ack and attempt "to dial out.

Another feature of" the invention-is. the. f

manner in which aftrunk-lineextending toia maln exchange. .1s .-markedbusy at the private automatic exchange when the trunk is' ta k'en.

for use atth'e main excl'iange Thetrunk is marked-busy by a highresistance relay atthe private automatic'exchange, which isCOIlIlQCll-'. ed to one '.conduc,tor of the. trunk? line andtto' ground.This jrelayis energized whe the trunk is first seized in series withthe.ring;

cut-off relay ofpthe connector seizing the. trunk at themaineX hange,andis energized in series with the back-bridge relay" of the connector,if the trunk is h'elclfromthe main exchange'after it the'p'rivateautomaticexchange. Y

has been 7 released at Theabove mentioned features and others 7 notparticularly mentioned at this time will be described in detail in thefollowing specification. with the 'aiol-of'the. accompanying.

drawingscomprising Figs. 1 and'fz. These drawings, whenFig. 2is placedto the right of Iilig. 1, illustrateby means of the usual Circuitdiagrams a schematic layout 'o fa private automatic exchangesystenrconnected by' means of two-way trunkli'nes with a main automaticexchange. i

The apparatus shown in Fig. 1, and that shown tothe left of the dottedvertical line in Fig2. is in the private automatic exchange," designatedP. A. X;, while thatshown to the f right'of the dotted vertical lineinFig.2 2,

located in the main automatic. exchange, designated M. A. X 1 Thetrunk'compIisingc0n:-.

ductors, 201 and 202 isoneof the'trunk's connecting the P. A. X. withthe M. A. X. At

theltl. A. X. this trunk terminates in the rotary l1nesw1tch LS and 1saccessible to a group of connectors, such'as connector C tical and rotart e havin an automatic ror tary movement on the level in which theinter-otiicevtrunk 'lines are accessible A cone nector of this type isshown and described in the Jacobson Patent No. 1,349,381, granted August10, 1920. In-the system chosento illustrate this. invention the mainexchange, is assumed to be an automatic exchange, though the privateautomatic. exchange-is equally capable of being connected with a manualmain exchange. 7 1

At the P. A. the trunk comprising conductors 201 and 202 terminates atthe attend ants cabinet in the jack J and is provided with a calllanipll and a busyvisual VIS.

The cord CC is one of a plurality of cord circuits provided for theattendant for completing calls from the M. A. X. for subscribers at theP. A. This cord circuit terminates in the plugs P and Pand is providedwith a connect and'ringing key RK, and a cord key CK for associating theoperators telephone set TS and the common equipment comprising thetelephone set relays TSR, the cord splitting key ,GSK, the dial key DK,and

the dial D with this particular cord.

One of the private automatic exchange subscribers lines, namely, theline of substation A, is shown, terminating in the lineswitch LS andhaving the individual line jack J The lineswitch LS may be of the'usualrotary type like the rotary lineswitch LS This lineswitch has accesswith other similar lineswitches to a group of selectors suchas theselector S. The selector S may be of the usual Strowger vertical androtary type, and

has access to a number of groups of connectors, such as connector C.

5 In one particular level, the selectors such as selector S have accessto the M. A. 'X. and in another level to key-ending trunks extending tothe attendants position. A In the banks of the connectors access ishad'to the individ u al subscriberslines.

:With this general description ofithe'efeatu'res of the inventionand-the apparatus in;

volved in mi'nd,'a further understanding of the invention may best begained "from a detailed description of the operations involved incompleting-connections. For this purpose it will first be assumed thatasubscribenat the M. A. X. wishes to converse with the subscriber atsubstation A. It will be assumed that the calling subscriber hasextended the connection to. the connector G which has been operatedto'seizethe trunk to the P. A. X. via the branch comprising conductorsthe trunk busy to the selectors.

separating'contacts 211 and 218 in the usual manner. 7

After relay 245 of connector C is operated, a circuit is closed for thebusy guard relay 110, at'the P. A. X. which includescontacts 101,conductor 201, conductor 201, and the upper Winding of the ringcut-ofi'relay 250 of the connector (3?. The resistance ofjrelay 110 issufli'ciently' high to prevent a suffi'cient' fiow of current in thiscircuit to cause the operation of the ring cut-ofl' relay 250 at thistime. Relay 110 atthe P. A. X. operates, however, and closesthelcircuitfor the busy visual VIS at contacts 111 to mark this trunk busy at theattendants position and'also closes a circuit'for relay 115 atcontacts112g Relay 11'?) operates and at contacts 116 grounds therelease conductor 206 to mark Relay 245 of connector C in operating,also causes ringing current'to be intermittently applied to'the trunkconductors, causing the operation of the ringing-response re lay 106bridged across the trunk conductors at the P. A. X. Relay 106, inclosing contacts 107, closes a locking circuit for its lower winding andalso closes a'circuit for the call lamp L The lighting of lamp Lapprises the attendant of the incoming call.

To answer the call, the attendant inserts the answering plug of an idlecord, such as plug P of cord circuit CC; into jack J As aresult, relay30 and-relay operate in series. Relay 100, in operating, disconnectsrelays and 106 from the upper talking conductor at'contacts 101, closesan auxiliary circuit for busy visual VIS at contacts 103, at the samebility of relay/106 being operated'and locking at the end of the callwhen the ringingbridge is again placed across the trunk conductors uponthe removal or plug P fromj ack J Relay 110 restores as soon as it isdiscon' nected from the uppertrunk conductor. opening theinitial-circuit of the visual VIS and the circuit of relay 115.Relayrestores atterwhich the trunk is marked busy by the presence ofground through the low-resistance winding'of relay 30 via contacts 117.

Relay 41 also operates when the plug P is inserted in the jack J fromringing current passing through its lower winding. This relay, inoperating, closes a locking circuit for its upper winding at contacts42, at thesametiineclosinga circuit for'the supervisory l'am'piL- r vAft-er inserting the plug P into jack J? the attendant operates the cordkey CK. iAs

aresult, relayl24 operates overthe circuit in cluding contacts 82 and81'. This relay con- 32being closed. The operation of key CK also closesa circuit for relay35 in series with relay 50, .the circuit includi11gcontacts-83.

The short-circuit around relay 35 is opened by theoperation of relayBOat contacts 83. Relay 35, in operating, opensthe circuit of lamp L andthe holding circuit of. relay 41 atcontacts 38, and connects the commonconductors 74 and 75 to the tip and ring conductors ofplug P. Aring-tripbridge has now been closed across'the trunk conductors forcausing the operation of ring cut-off relay 250 in the connector C2,vwhich extends from the tip of plug P, contacts 36, conductor 7 5,

1 upper normally closed contacts of keys DK and CSK,.c0nductor 71',contacts 87 and 27, the upper right hand. winding of repeating coil Rcontacts 25, and 32, the lower right hand Winding of repeatingcoil.R,=contacts 28 and 88, conductor 72, lowerinormally closed contactsof keys CSK and DK, conductor 7 4, contacts 39, to the ring of plug P.Relay 250 therefore operates and trips-the ringing inthe-usual mannerand closes points in the talking connection. The back-bridge 255 thenoperates over thetwo trunkronductors and the bridge across the tipandring of plug P with the usual results.

Relay 50, in operating in series with'relay' 35, opens a point in thereceiver circuit at contacts 51 and closes a circuit for relay 55 atcontacts 52. Relay 55 operates and closes a pointin the receiver circuitatcontacts 56,- closes a'holding circuit for itself at contacts 57, anddisconnects relay '50. Shortly after its circuit is opened, relay 5'0deenergizes andby clos1ngcontacts51 closest-he receiver 011- cuit.Thereafter relay 55 is held energized in serieswithrelay 35-. By sodclayingthe closureiofthe receiver circuit. until some time after thering is tripped and the current over the trunk conductors has becomesteady, annoying clicks in the receiver are prevented. The'attendant maynow converse withthe calling-subscriber at. the mainautomatic eX- changeto learn the name of the subscriber with whom connection is desired.After obtaining this information, the attendant touches the tip of theplugPitothe sleeve of jack J (having assumed that the subscriber atsubstation A is the called subscriber) to test the line for the busy oridle condition in the usual manner. Finding the line idle, the

' attendant-inserts plug P into jack J. Relay D 2 operates inserieswith. the-.cutoff :rela-y '97 the circuit of the of the lineswitch LS,closingpointsin the:

contacts 5.

After inserting plug .jack J, the 555,,

tendantoperates key RK'tothe right .topro-Q talking circuit at. contacts4-an'd 6, and closing.

supervisory lamp Lat] jectringing current out on the calledsub fyscribers line. contacts 14 and .19, and contactsf4and 6 5 When thesubscriber. at substation. A

answers by removing his receiver, acircuit is closed for battery feedrelay 10 Relay 10, in operating,.opens the circuit oflamp L at contacts11 and prepares a circuit for re:-' 7, I

lay 15 at contacts 12. The extinguishment of lamp L notifies theattendant that the called subscriber has answered.

Before completing the talkingconnection V with the calling subscriber,the operator may common cordsplitting key CSK to theright.

This operation disconnects .thecommon leads 74 and 75 from the operatorstalking; conductors 76 and 77, and at contacts 84 places a holdingbridge including resistance 85 across the tip and ring conductors.Operating key CSK to the right also opens the circuit of relay'24atcontacts 81. Relay. 24,..in deenergizing, connects the common talking.leads 71 and 72 on the tip and ring conduc-- tors of plugP atcontacts-26 and-29 via con tacts on the ringing key RK. The attendantmay now speak with the subscriber at substation A' without the callingparty hearing. the conversation. If the subscriber at substation A doesnot wish to speak with thecalling subscriber, the attendant by again re-The ringing circuit includes.

key OK to disassociate her'head'set and. common apparatus from thecordcircuit-CC.

Operating'key RK. momentarily to the. left closes a circuit for relay20.. Relay 20 energizes and closes a holding circuit for ie I "lay. 24at contacts 23, closes a point in talking connection at contacts 22, andcloses aholding circuitfor itself inseries with relay 15 at contacts21.v Relay'15 operates and'at contacts 16 and 18 completestheftalkingcircuit, and byseparating contacts 14 and. 19 disconnectstheoperating springs of the ring:- ingkeyRKifrom conductors 95 and 96*.The calling and called subscribers mayfn'ow cons verse with each other.restored, the talking circuit extends through the springs of keys CSKand DK. When key CK. is: restored, the. circuit of; relay; 35

Before key or; is

and relay 5:5 is opened at con'tacts831 Relay 55vinrestoring, places thetelephoneset-relays TSRin their normal condition. Relay 35, in.,deenergizing, connects the talking conductors 93 and 9a to the tip andring otplug P directly, thereby. completing thetalkingcircuit' betweenthe calling and the called subscriber completed, she may do so by againasso.ciat-' ing/the'common equipment including key CSK with the cordcircuit CC by operating the cord kcv GK, and then operating key CSK tothe right or left depending 'on which party she wishesto speak with.Throwing key CSKto the left disconnects the common talking conductors 71and 72 from theopen ators talking conductors 76 and 77, and also openspoints in the holding circuit across the tip and'ring ofplug P extendingthrough the springs of key CSK whenever key CK is operated,but'asubstitute one is provided through the secondary windings oftheoperators induction coil when condenser 78 is short-circuited atcontacts 86.

At the termination of the conversation both subscribers will replacetheir receivers. Responsive to the replacement of the receiver atsubstation A, relay restores thereby opening the circuit of relays andat contacts 12, and closing the circuit of super-' v'sory lamp L atcontacts 11. Relay 15, in deenergizing, again opens the talking circuitat contacts 16 and 18. Relay 20, in deenergia ing, opens the holdingcircuit of'relay 24. Relay 2% deenergizes and at contacts opens thedirect current bridge across the tip and ring conductors of P therebyopening the circuit of back-bridge relay 255 of connector C at the mainautomatic exchange. The release of back-bridge relay 255 in the wellknown manner causes the release of the connect-or C2, providing.thecalling subscriber has previously replaced his receiver If thecalling party, however, does not replace his receiver, the connector Cas well as the other automatic switches usedin the connection, will notbe released until he does so, as is well known I v, I

Should-the called subscriber again remove his receiver .after he hashung up, even though the plugs P and P are in jacks J and J and thecalling subscriber is still holding the'connection' to the P. A. X. notalking connection can again be completed since relays 155ml 20 arede'energize'd. Of course, if the attendant again operated keyRK to theright thetalking connection would be completed as previously described.The lighted condition of the lamp L after conversation has taken placeindicatesto the attendant-that the conversation is terminated.

She will then remove the-plugs P and- 'P of 100 in deenergizing' againplaces the trunk to the'niain exchange in normal condition. If,

. however, the calling subscriber is still hold ing the connection,relay llOwill again oper-. ate, this time in serieswith the upper winding of back-bridge relay 255 of co-nnector'C Relay 110 will againfunction to operate the busy .visual'VlS, and mar; .thetrunk busy to-theselectors. 1 2" As noted above, the trunk is marked idle at the M. A. X.as soon as both the'calling and the called partyreplace their receivers."For I this reason a second call can be extendedfrom themai-n automaticexchtngeto the private automatic'exchange over the trunk comprisingconductors 201 and 202 before the attendant has removedplugs P and Pfrom jacks J and J after the termination of acall. such a case theconnector seizing the trunk causes the operation of relay 110 andprojects ringing current over the trunk conductors as previouslydescribed. Again relay 41 responds, closing the circuit for lamp L and aholding circuit for its upper winding at contacts 42. The lighting ofthe lamp L at this time notifies the attendant that a second call hascome in over the trunk, while the li hted condition of lainp L indicatesto her that the previous connection has been released. It shouldbeparticularly noted that ringing current over the trunk conductors 'atthistime cannot resignal the-subscriber at substation A in whose jackthe plug P rests, since'the talking connection to the subscriber atsubstation A was opened upon the releaseof relay 15. The attendant maynow answer the second call inthe regular manner. The presence'of plug 'Pin jack J has no effect. After learning the wants of the callingsubscriber she may remove the plugP from jack J' and insert it into theproper jack andcall the calledsubscriber as previously described.

If the attendant, after receiving an incoming call fromthe mainautomatic exchange knows that the called subscriber is waiting for acall from this particular calling sub scriber, it is unnecessary for herto first speak with the called subscriber. She may call the calledsubscriber by operating the ringing key BK to the right (having set upthe connection to the called line by inserting the plug Pinto'the j ack;J) and immediately op- "erate the key BK to the left momentarily beforethe called subscriber answers. Theoperationfof key RK to the leftprepares the cord circuit CO in such a way that the talk ing connectionwillfbe established as soon as the called subscriber remove hisreceiver. This operation closes the circuit for relay 20 which again'operates and closes a locking circuit at contacts 21,-th1s;t1me over acircuit including contacts .13., 17, and 5, relaylO not being energizedbecause the called subscriber has not yet answered. After'operatingwthel-tey Elite the left nionientarily,f the attendant may disassociate 'hercommon: equipment including her "telephone set itroin the; cordcircuit'GC'by restoring key GK and attend to other call s. dVhen the:called subscriber answers, relay again energizes 'and byclosingcontacts: :12 again causes "the operationz'of-relay 15in series withrelay 20, With the results aspreviously described In this system it .isalso possible for any :of the'subscribersisuch as thesubscriber .atsubstation A to extend a call to the automaticjex changeover Zone oftheinterconnect-ing trunk lines, these trunks being accessible inapartlCll1!JI l8'V.l IiIl/thGfbilIlkS of the selectors.

Forexample," when a call is extended from.

the vsubstation-A.-Via the. individual .lineswitch LS and the .selector.S tothe trunk line comprising conductors .201. and 202 by Way of thebranchfcoinprising conductors204 to 206, the 'lineswitch LS operatesinthe usual Way and extendsithe connection to a selector in the mainfautoma'tic exchange. When the trunk line is seized, ground potential isplaced onrelease conductor 206 thereby closing a circuit "for rel'aylOO. Relay F operates and' disconnects the 'ringingbridge from 1 acrossthe trunk} conduoto'rsiat contacts 101 and. :Jand closes acir'cuitiforthebusy 7 visual lSgati'contacts 103; "Re'lay. also operates in serieswith the trunk conductor 201 and at c0ntactsii126-fcl'oses a'circuit forrelease relaylZO. iR'elay 120 directly grounds release con j uctor 106at contacts 121- to main tain the automatic switches in the P. A. X.operated "and imaintainv this trunk marked busy. The subscriber"at'substation .A, by

dialing the proper "number controls the setting up of theconnectionintheusual manner. When the subscribers replace their receivers at thetermination of the call, the operated automatic switches'at the P. andthe .60 I the lamp L? indicates to the attendant that someiin-iorm'ationis wanted. Toanswer the call the attendant operates key K .As a resultVreIa yZQGO is operated over the circuit including 7 contacts 28i. -lhelamp L. as ex:

tinguished; Atcontacts 282, a circuit is closed :for relay 6510f the(telephone set rela s w'IS-R. Relay-65, inenergizing, connects t etelephone circuit to the common conductors 291,292, and; 293; Atcontacts "68, aci1fcuit causesfthe energization-of-relay 155, with theresults previously described. 7 y In the systemdisclosed, an attendantmay also [set up =.a; so-called' tail-to-tail connection; that is,should she be asked by one of the P. 'subscribersgto set up a connection for him-to the M. A.'X. she'may insert the plug P into-the jackof'an idle trunk extending to the main automatic exchange, suc'ha-s thejack J2 for example, then operate the corresponding cord key CKgthenoperate-the common dial key vDK, and-then dial the desired number.Inserting the plug P i'ntojack J againcloses a-circ'uit, for relays i30-and-'-100- in series. These relaysoperate, performing the samecircuit changes as previously described; The operation'of keyGK closes acircuit of relay-.35 which operates and connects conductors 74'and 75'to. the

tip andring of plug P. :Operatingthe-dial key DKbrides the dial D acrossconductors 1 74 and 75.

manner. This selector and .otlierautomatic l ines-witchLS operatesandfe'x-' tends-the-connection to a'selectoringtheusual j switches intheinain "automatic exchange re: spond to the "mani ulations ofthe-dial; D in accordance Withthe call-ed'subscribers inums I berjtoextend the connection tol the called After setting up *the connection tothe called subscriber the attendant may call the A. X. {subscriber whorequested theconline.

nection in the same manner-as 'though'the call had beenfinitiated .bythe called-subscriber rat themain automatic exchange. In this case, shemay-also operate the key BK mo- 'mentarily tothe left immediately anddisassociate the common equipment from the cord circuit by restoringrkey' CK before swered,-or.she'mayiconverse "with the P; A. X.subscriberafte'r he answers without the other'party hearing theconversation the same as previouslydescribed. I V

-Aparticular characteristic of-this inven tion is'that should anattendant attempt to extend a call to. a P. A. X.. sulbscriber alreadybusy in another connection'or engaged in theprocessbf setting up aconnectio'n, the plugging in of' 'the plug of'acord i-ntohis line jaokwill .not interfere with the exist ing connection or with thesetting'up ofthe other connection; For example, should the attendantlinsert plug .P into jack J. (ignore ing the busy test while thesubscriber at sub; station. A isjengaged .insetting up automatic Vswitches inf'the P; A. X., relay 2 could not operate vsince directgroundpotential would be present gathesleeve Qt J. Inthi either thecalling -or called partyhas an- 70 is also closed for fire-lay 50whichenergizes and case lamp 'L would not light whichwouldfurtherindica-te to the attendant that the line wasbusy'. Evenifshe alsoignored this indication and attempted to ring'by-operating key RK'to-the left, no ringing-current could be projected out on the connectionby reason of the open condition of contacts 4 and 6.

-It is also'impossible for the attendant to project ringingcurrent onthe called line I after-the talking connection between thecallingandcalled subscriber has been completed. 'When relay -15 0perates andcompletes the talking-connection, the ringing leads are disconnectedfrom conductors 95 and 96 at contacts 14 and 19. Thereafter anyoperation of key BK is ineffective.

' Furthermore, the attendantcan not interfere with theYsetting-upofaconnection to the main exchange by the calling P. A. X. subscriber byinserting plug P into the jack of the'trunkextending to the mainexchange over whichthe connection is being set up. For example, shouldthe attendant insert plug P into jack J while the subscriber atsubstation A is engaged in the process of setting up a connection to themain automat-i0 exchange overthe trunk comprising conductors 201- and202, no harm would resu'lt; Since ground potential would be present'onjack J relay '30 could not operate in series with relay 100. WVith relay30 renaining in a 'deenergized position relay wouldremainshort-circuited at contacts so that throwing cord key GK and thedialling key DK would not bridge thedial' D across the tip and ring ofplu-giPl By relay 35 remaining in a deenergized condi ti'on the tip andring of plug P remain connected to conductors 93 and 94c. Throw-- ingkey CK would, however, cause the operation of relay 2a and the operationof relaysand as previously described. The attendantis head set wouldthen be r bridged across the tipand ring of plug'P so that she would beadvised of her error by hearing clicks produced by the diallingoperation or byhea'ring the conversation. v r

' This completes the description of the op eration of the invention.Whatis considered new and is -desired" t o have protected by LettersPatent is specifically stated in the appended claims. f

'jVVhat is claimed is:

p 1. In a'telephone'system, a line,a cord cir relay in said cord, meansoperable at will for operating said self-locking relay, a second relayresponsive to the answering of the call, and means for connecting saidsections jointly controlledby said self-locking relay and saidsecondrelay.

p -3. Ina telephone system, aline, a cord circuit comprising twonormally disconnected sections, means for connecting'said cord circuitto said'line-to extend a call, a key, means responsiveto a.momentaryoperation of said key after the subscriber at the station on. the linehas removed his receiver to answer the call for connecting saidsections, and means responsive to the replacement of the receiver fordeactuating said last means so that-it cannot again be operated shouldthe receiver again be removed until'saidkey'is again oper ate 14:- Inatelephone system a. line, acord circuit-comprising 'two normallydisconnected sections, means for connecting said cord circuit to saidline to extend a call, a key, and means responsive to the answering ofthe call providing said keyYis-operated before thecall is answered, and:responsive to the operation of said key providing the'c'all is Vanswered before the key is operated, for connecting said sections.

' 55in a telephone system,'a cuit' comprising two normallydisconnectedsections,-means for connecting said cord circuit to :saidrlineto extenda call, means for signalling the subscriber on saidpline, key

springs, and means responsive: a momen-' taryoperat1onofsa1d key spr ngsafter the call is answered for connecting said sections and .fordisabling saidr'signalling means.

-6. In'acord'circuit comprising two normally disconnected sections, aringing key and leads; extending from said key to the talking strands ofthe, cord-circuit, a relay for connecting said two sections;.andcontacts son-said relay for disconnecting said leads from saidtalkingstrands zpi 7, ,In 'a telephone systein,; -a cord circuit havinga.-fir st and, asecond plug, a pair of talking conductors having twobranches, means for connecting the first branch-,to'the first plug,means for disconnecting the first branch from the pair of talkingconductors, and meansresponsive to said .last means for connecting saidsecond branchto said second plug. I V

- 8. In a telephone system, a cord circuit,a pair of "talkingconductorsf having two branches, a key in said cord, connecting meansresponsive tothe operation of said key undercertain conditions forconnecting the-first branch to one end-of said cord cirline, a cord cir-1 cuit, means for maintaining said connecting I i nveogom cuit,providing :said connecting n1eans are maintained IDQP'GTa tWQ.

- 9. in a telephone system, I a i plug ending cord cirouit, a jackending {tr-unk, a pair of talking "conductorg apair-aof controlconducltorsa key, and means responsive to :the oper' ation of said keyafter the pl-ug of said :cord

i'siinserted into fsaid j a'c'kfor-"connectingsaid control conductors to-sai'd plu g, providing said trunk idle, and for connecting said;

talking conductors to s'aitl plug, providing the trunk is busy.

10. In a telephone system, a first exchange, a second exchange, aninterconnecting trunk line, a switch at said second exchange havingaccess to said trunk, a ring cut-ofi" relay inv said switch, a busyguard relay at said firstv exchange connected to one conductor of saidtrunk line and to ground, and energized inseries with said ring cut-oflrelay responsive to the seizure of said trunk line by said switch in theextension of a call to said first exchange, means cont-rolled by saidbusy guard relay for marking said trunk line busy at said firstexchange, a' ringing bridge including a ringing relay across theconductors of said trunk line at said first exchange, means in saidswitch for projecting ringing current on the trunk conductors to operatesaid ringing relay to signal an attendant at said first exchange, andmeans responsive to the answering of the call for disconnecting saidbusy guard relay, for opening said ringing bridge, and for operatingsaid ring outoff rela r 11. n a telephone system, a first exchange, asecond exchange, a connector at said second exchange, ,aninterconnecting trunk line accessible to said connector at said secondexchange, a ring cut-ofi relay and a back-bridge relay in saidconnector, a busy guard relay at said first exchange connected vto aconductor of said trunk line and energized in series with said ringcut-ofl' relay responsive to the seizure of sald trunk by sald vconnector to extend a call to said first exchange, means fordisconnecting said busy guard relay from said conductor and foroperating said ring cut-01f relay when the call is answered and forreconnecting said busy guard relay to said conductor at the terminationof the call, said busy guard relay being energized in series with saidback bridge relay upon its reconnection to said conductor, and meanscontrolled by said busy guard relay for marking said trunk line busy atsaid first exchange.

12.'In a telephone system, a first ex change, a second exchange, aninterconnecting trunk line, one conductor of said trunk being normallyconnected to ground at said second exchange, a busy guard relay at saidfirst exchange connected to said one conductor and to ground, anautomatic switch at said second exchange having access to said ;t run kline, a battery having one'poleconnect- "ed to ground, a ring'icu't -ofirelay in said switchconnected to theungrounded pole of said battery,me'ansresponsiveto the seizure of saidtrunk'by' 'saidswitchin'theextension q seriesconn QtedacrOSSthe conductors of 'said -trt1=nklin e, .-means for extending a conne'c-t-ion over said trunk'line andforprojectin-g rings ing cu-rrent over the conductorsof said trunk lineto operate-said relay, -.rneans for dis'conmeeting said bridge -fromsaidcon ducto-rs aud torshort circuitingasaid condenser fwhen saidlbri dg \Vacross said-conductors,atthe-termin-ation oifthecall.

1 145. In a stelephone system, a 'trunkline, a bridge includinga relayand acondenser in seriesgconnected across-the conductorsof said 7x-trun-k line, 'meansz-foi ext ending a connection over. sardtrunkqhneand for pro ectrng ring- 'l ng current overrthe conductors-of saidtrunk 4100 disconnectingnsaid :bridge when-the call is line vto operate.said relay a second-relay 'fo-r answered-and for reconnecting csaidbridge the-call r-is i rll w-ered and for reconnecting across saidconductors atthe termination of rlllle I call, and contacts on @saidsecond relay for short-circuiting said condenser when the calliisanswered ..t.ordischarge the same to elimi-nate t-he ,poss'ibilityvofsaid first relay being operated by 1a idischarge otsai'd .con-

denserwhenfthe bridge is reconnected across said conductors. a. f: A1-15, a telephone syst,en1,\.a cord circuit for answering and extendingcalls, apa-ir oi":

talking conductors, a.-'double-throw, cord- I splitting-ikeyfforassociating said rtalking conductor s'with either endof said cord 1circuit to the exclusion of the-other, means responsive tothe answeringof a call :Eor connecting a direct current bridge across the conductorsof one end corJd, said bridge -includ=ing normally closed contactsonesaidjkey, other contactslonn'said key for providing a substitutedirect current bridge including said talkingeconductors in serieswhen-said first bridgefis' opened bythe opera- -tionof said key fin onedirection, a f'resistance, --andho.ther contacts on sai'cl key for-p'rovi dings a substitute ".(llIBCl', current :bri-dge includingisa-i'd resistance .when said first bridge isopened by theoperation ofsaid key inthe other direction. 1

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fa trunk accessible tosaid cord circuit, a pair of dialling conductors,a key, -mean's controlled by said key-for connecting said con- (Motorsto the cord circuit, provided said trunk is idle whenconnected with, andmeans effective in case the-trunk is busy for rendering said meansnon-responsive to said key.

'17. In a telephone system, a cord circuit, a trunk accessible to saidcord circuit,'a pair of dialling'conductors, a key, means controlled bysaid key for connecting said conductors to the cord circuit, providedthe trunk is idle when connected with, meanseiiective in case. the trunkis busy lforrendering said means non-responsive to saidkey, and meansfor extending a connection to a called line,

a ringing key fortransmitting ringing. current overthe called'line,aa,frelay controlled by the called subscribenaa second relay con-192s.,- I v THOMAS r. onoo controlled by said key for notifying the op-V erator of the busy condition of said trunk,'-

":18. In a telephone system, two-way trunk, aconnectorswitchfor'connecting with g said trunk at one end, nieans'in saidconnectorjior ringing over the trunk. means in said connector forestabl'lshlng a'direct currentcircuit over only one conductor of thetrunk'andior maintaining the same while the ringing operation-isproceeding, and a busying relay at the distant end of the trunkcontrolled over said direct currentcircuit.

19. In a telephone system,atwo-w ay trunk line,a connector for seizingsaid trunk at one end, two circuits established by said con necto'r onseizing the trunk line, one circuit including both conductors ofthetrunk in series and a source of ringing current and the other circuitincluding only one conductor of the trunk and ground, a ring-cu't-ofirelay in said connector included in both said circuits, and busyingmeans at the distant end I of the trunkcontrolled over. said grounded vcircuit. 'r I 20. Ina telephone system, a two-way trunk line, aconnector for seizing said trunk line I at onev end. means in theconnectorfor connecting a ringing current source to one-conductor ofsaid trunk line, a ring cut-oii relay in said connectorconnected'between the'other ccnducgor of the trunk and the exchangebatteryin readinessto cut off the ringing cur-rent when the call isanswered, and husying means at the otherend of the trunk line operatedby current supplied over the said other trunk line conductor throughthe" winding o f said ring cut-ofi relay. A i c a a 21. In a telephonesystem,.a cord circuit for connecting a calling and a called line, adouble-throwdzey in said cord circuit, means responsive to the operationof said key in one direction for transmitting ringing current over thecalled line, andmeans responsive to the operation of said key in theotherdirection after the calledsubscriber has answered for renderingsaid-key ineffective in case it is reop'erate'd' ingsaid firstdirect-ion.

